I don't know about you or anyone else but I think Mages rock in this game (when it comes to PvP at least). In fact, I distinctly remember one Guild War I was in that I just dominated. I was level 24 or close to that and we went up against a Guild that had a few level 20s and two level 30s. One of the level 30 guys was a Fighter and the other was a Cleric. Anyways, I was dispatching most of the level 20s with relative ease and then came the level 30s. The Cleric I only managed to kill once and i'm still not sure how I did it but I killed that level 30 Fighter several times.
I had to spam my stones and potions like crazy but it was well worth it when I practically dominated the entire Guild by myself. Eventually my Guild stopped but I kept going and then their Guild stopped (sort of) and they all just ran off. It was the happiest moment of my Fiesta life to see them run away from me or die by my hands. Of course, I can no longer do that but it was fun while it lasted. There really is no strategy or trick to it. Just spam the hell out of potions, stones, and spells. Oh and of course... having a Cleric around helps a lot too, lol.